Dust and spillage prevention

Paul Boughton

A report on how the latest dust and spillage prevention technology can help to improve both environmental issues and production

Ore and coal materials handling technologies that solve major dust and spillage problems while also boosting production are being advanced by an Australia-based engineering group as a solution to issues increasingly confronting Australasian and international producers.

Chute Technology packages – employing the best current technologies developed from proven installations in alumina, iron and other mineral ores and coal handling facilities at mines, energy plants and ports – tackle dust problems at their source rather than attempt to control dust after it has been created and dispersed into the atmosphere.

The same technologies can be applied to inlet, hood, chute, spoon, enclosure and saturation zones to address widespread spillage hazards, with their cost, downtime and safety issues. Chute Technology engineer Dennis Pomfret comments: “Good designs such as these – either new or retrofitted – demonstrate that environmentally sensitive production need not necessarily come at a cost to output.

“In fact, these chute improvement technologies have achieved major increases in production, exceeding 50 and even 80% in some cases, while solving waste and spillage problems. We have unified the best proven technologies that address dust and spillage issues and combined them into problem-solving packages that combine: integrated advanced product flow analysis; 3D discrete element method (DEM) design processes; and globally proven manufacturing services.”

Pomfret adds: “The packages deploy technologies whose availability and application may have been too fragmented or unmanageable and put into the ‘too hard’ basket. But now the environmental safety and profit waste issues raised by dust and spillage have placed these issues high on the industry agendas worldwide.

Transfer control stations

Chute Technology’s dust and spillage technologies feature dust-minimising transfer control stations on material handling conveyor belts, as a component of energy efficient and water-conserving technology packages for new and retrofit loadout facility projects. The new transfer stations and associated downstream technology minimise the amount of dust created in the first place, reducing water needs as well as energy required for dust collection fans and filter houses. They contain whatever dust is created within the transfer point, minimising harm to the surrounding environment.

The new transfer technologies also curtail spillage and optimise conveyor belt width loading potentials by eliminating the disruptive steep drops and turns in conventional chutes that cause dust, blockages, spillage and wear.

“Instead of having huge energy-sucking extraction installations to collect up dust that escapes conventional chute designs, we cost-effectively engineer new transfer stations based on passive dust control principles with de-aeration chambers,” explains Pomfret.

In-service examples of the technology have cut dust emissions from 2700mg/m3 in the transfer station on a 650tph alumina conveyer in Australia to well within the client’s target of less than 1000mg/m3. In addition, the heavily reduced dust load was contained within the transfer station, rather than allowed to be able to escape to the atmosphere and onto surrounding valuable arable land.

The company reports that outstanding results have also been achieved on ore and coal installations, including a power station coal feeder in the USA where new chute systems, engineered and modelled to achieve design flow rates of 1,000 tph, increased throughput nearly 50% while reducing spillage and dusting in the yard by 98%.

The Chute Technology engineering group targets problems common to many coal and ore plants and loading systems by addressing them with the combination of three skill sets, comprising advanced engineering analysis of flow from Dennis Pomfret Engineering, followed by upscaleable 3D DEM design processes from Chute Technology partner Mckajj Services and custom manufacturing to individual plant needs by partner TW Woods.

The combined technologies are complemented by the practical experience of each of the three principal partners in Chute Technology, who have combined experience of more than 80 years in a wide variety of resource industries including coal, iron ore, alumina and limestone across Australia, the USA, South America and South Africa. The technologies are also applicable to gold, nickel and other bulk minerals and ores.

Design solution

The main design solution elements, varying from project to project, include improvements in a number of areas. First is in the inlet area. The approach to dust abatement in this area is a headchute enclosure to limit the inflow of entrained air by the use of overlapped curtains.

Next is the hood and intermediate chute. This area is redesigned to ensure material trajectory is at an optimal angle, with respect to impact forces and material flow (wall friction is used to retard the flow speed). The sides of the hood are shaped in to contain the accelerating material and thereby minimise the expansion effect caused by free fall.

Design improvements can also be made in the spoon area. Redesign of chute spoons focuses on more smoothly turning material into the direction of the receiving belt, while more closely matching the speed of the exiting material to that of the receiving belt. “Changing the particle dynamics in this area is important because, when a vertically falling particle lands on to a moving surface – i.e. the belt – a motive force is suddenly applied to one side of the particle,” says Pomfret. “The inertia of the particle resists acceleration in the direction of the belt.  Instead, it generates a rotation in the particle, which may have a tangential velocity that is faster than the speed of the belt. Consequently, the particle ‘bounces’ in the opposite direction to the belt travel.

“This counter rotation motion of material in the loading zone generates a highly agitated – and therefore highly aerated – product. The action leads to dust otherwise bonded to being expelled into the free air.”

Material is guided so that it is not flowing sideways into load zone skirtboards – wearing them and prompting seal failures – but rather running parallel with them.

With regard to the spoon deration chamber, for superfine materials, a deration chamber to allow reconsolidation of the material to normal density from the low density developed during free fall.

Meanwhile the chute recirculation enclosure is designed to minimise the entry of new air into the transfer by eliminating the need for low pressure zones to draw air into the system. This pressure differentiation effect is overcome, where required, by connecting the high pressure zone to the low pressure zone and setting up a recirculating air path.

The final element to consider is the load zone enclosure. Here, a long chute extension with soft seal skirtboards and overlapped internal curtains to allow entrained dust laden air to resettle on the outgoing material stream.

“Any or all of these elements can be incorporated into new or retrofits, depending on system needs,” says Pomfret. “Sometimes we find that a total redesign of existing systems isn’t required, because just two or three components of the transfer are mainly responsible for creating the dust load.

“Mining and energy companies, as well as port loadout facilities, may have been able to afford built-in inefficiencies when resource prices were high. But as the emphasis switches to higher production for lower cost, accepting old standards of inefficiency is no longer an option.”

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